National Weather Service Survey & MapsRyan and I met Brian and moved near our target area around the IA, NE, SD border intersection. The storms developed in the early afternoon and Brian had us on top of the cell of the day in McCook County South Dakota as it began to tornado. We watched the full cycle of the 20 minute long tornado including the crossing of Interstate 90 (pictures 1-5). Then saw a second tornado (picture 6) destroy a farm stead in Minnehaha County South Dakota. Best chase of the year.